Photographic colloid transfer process



3&4353? Patented July 10, 19-62 3,043,687 PHDTOGRAPHEC CGLLGED TRANSFER ERQQES John W. Liege, Rochester, Nit! assignor to Eastman Kodak Company, Rochester, N31, a corporation of New lersey No Drawing. Filed May 4, 195 Ser. No. 810,575 2 Claims. (Cl. 96-28) This invention relates to a process in photography wherein an image in soft adhesive organic colloid is formed photographically and a discrete stratum of the image is transferred to a receiving sheet to provide a reproduction of the subject. The process is described in the Yutzy et al. U.S. Patents 2,56,756, granted May 3, 1952 and 2,716,059, granted August 23, 1955 and em bodies the exposure to a subject of a substantially unhardened gelatino-silver halide emulsion layer which may contain a gelatin tanning silver halide developing agent as well as a non-tanning silver halide developing agent. Upon activation of the exposed emulsion with an alkaline solution in the presence of the developing agent or agents, tanning development of the more exposed regions of the emulsion corresponding to the highlights of the subject proceeds although some development of the less exposed regions also takes place to provide visual density for the transferred image as explained in more detail in U.S. Patent 2,716,059 above. Thereafter the developed emulsion is pressed into contact with an absorbent receiving sheet such as paper to cause the less exposed regions, and thus the less developed regions, of the emulsion .to adhere to the receiving sheet. Subsequently, when the emulsion and receiving sheet are separated a stratum of the less exposed regions of the emulsion remains on the sheet and appears as a positive silver image of the original subject.

As mentioned in the above patents,,the alkaline solution used for activation of the exposed emulsion layer advantageously contains a gelatin-softening agent to facilitate transfer of the less exposed portions of the emulsion to the receiving sheet. Urea and certain other gelatinsoftening agents have been suggested for the purpose. The above patents also suggest the use of sodium carbonate as the alkaline component of the alkaline solution used for initiating development of the exposed emulsion.

I have discovered that in the described process a distinct advantage resides in replacing urea and sodium carbonate by acetamide and potassium carbonate as the gelatin-softening and alkaline components respectively of the mentioned solution. That is, the solution of urea and sodium carbonate has the undesirable property of readily crystallizing out on processing equipment used in commercial installations and eventually rendering movable parts, particularly of continuous processing equipment, difficult or impossible to operate. Thus a squeegee blade or roller designed to press the sensitive element against the reception sheet in the transfer step may not impart the proper pressure and a print of inferior quality results. Also, an accumulation of chemical dust resulting from the crystallization of the compounds on the equipment and adjacent surfaces may have an adverse effect on the photosensitive emulsion and the general health of the operator.

When the combination of acetarnide and potassium carbonate is used in the alkaline solution these troubles are substantially eliminated. The solution does not readily crystallize out on the processing equipment, particularly since concentrated solutions of the compounds are liquid at much lower relative humidities.

The following example will serve to illustrate my invention.

A substantially unhardened gelatino-silver halide emulsion (having a hardness as defined in the above patents) is prepared as described in U.S. Patent 2,716,059 above and containing a mixture of tanning and substantially non-tanning silver halide developing agents such as 4- phenylcatechol and 4-methoxy-a-naphthol. The emulsion is coated on a paper support and dried. The resultant sensitive element is then exposed to a two-tone subject (a line or halftone subject) if desired by reflex methods, and placed in the following alkaline solution of the invention to initiate development.

Potassium carbonate (anhyd) grams 34.0 Acetarnide do 40.0 Water liter 1.0

When hard waters are used in making up the above solution, in order to prevent the formation of scale on equipment it is advisable to add a Water softening agent such as well known alkaline earth metal chelating agents, e.g., ethylenediaminetetracetic acid, dior tetrasodium salts. About 4 grams of the salts are useful in the above formula for this purpose.

While development in the above alkaline solution is proceeding, light should be excluded to the extent required by the particular silver halide present in the emulsion. With daylight working emulsions limited exposure to room lights may be given during the exposure and development steps. Other emulsions may require the use of the usual safelights during the exposure and processing steps. When the proper amount of exposure has been given, gelatin tanning silver halide development occurs principally in the more highly exposed areas of the emulsion and little or no tanning development in the other areas. When development is complete as determined by trial with the particular emulsion and conditions of operation in use, the sensitive element is pressed into contact with an absorbent sheet such as paper by means of a squeegee blade or rollers. Immediately thereafter the sensitive element and receiving sheet are separated leaving a stratum of the less exposed and thus less hardened regions of the emulsion adhered to the receiving sheet. The result is a positive line or halftone silver-containing image afiixed to the sheet. If desired, the transfer operation may be repeated at number of times by merely rewetting the sensitive element in the alkaline solution and squeegeeing to a fresh reception sheet.

The reception sheet for the process is advantageously prepared as described in the Chan et a1. U.S. Patent 2,865,745, issued December 23, 1958 comprising a paper sheet on the surface of which is a mixture of an intensifying agent such as thiourea and a development suppressing agent such as sodium formaldehyde bisulfite.

The quantity of acetamide and potassium carbonate in the alkaline solution may be varied from that given in the above formula depending upon the requirements of the particular emulsion used in the process and the conditions of operation such as temperature; less acetamide being required at higher operating temperatures. Thus, while the emulsion should have a minimum hardness of the order mentioned by the above patents corresponding to a gelatin layer containing about 0.7 gram of dry formaldehyde per pound of gelatin freshly coated, more or less acetamide is required at diiferent operating temperatures. Similarly the optimum amount of potassium carbonate may be readily determined by experiment with different emulsions, development times, and temperatures. Since the potassium carbonate furnishes the alkaline component of the solution, development is accelerated by use of higher amounts and conversely by lower amounts. Also, too much potassium carbonate should be avoided, otherwise the emulsion Will be unduly hardened during the development step.

l J) In a preferred embodiment of the invention the gelatin tanning and non-tanning developing agents are present in t the emulsion. However, either or both developing agents may be present in the alkaline solution and the other in the emulsion. A very useful combination of developing agents is 4-phenylcatechol with 4-methoxy-a-naphthol. Since the latter is self-coupling it forms a colored compoundiduring development which contributes density to the print. Other useful tanning and non-tanning silver halide developing agents are disclosed by the above patents.

Guanidine carbonate may be used as the alkali in the solution used for initiating developing in the processes of the above patents, but is not as satisfactory as potassium carbonate from the viewpoint of preventing crystallization of the solution.

What I claim is:

l. A method of photographic reproduction which comprises exposing to a two-tone subject a substantially nonhardened gelatino-silver halide emulsion layer, said emulsion being not harder than a gelatin layer containing 0.7 gram of formaldehyde per pound of gelatin freshly coated, developing said exposed emulsion layer With a solution of potassium carbonate and acetamide in the presence of both a gelatin tanning silver halide developing agent and a substantially non-tanning silver halide developing agent to obtain a hardened gelatin and silver image in the areas of the emulsion layer corresponding to the highlights of the subject, and substantially unhardened gelatin, silver and silver halide in the areas of the emulsion layer corresponding to the shadows of the subject, said development being such as to prevent any substantial tanning of the emulsion layer in said areas corresponding tothe shadows of the subject, pressing a sheet having an absorbent surface against said emulsion layer while said emulsion layer is moist to cause only the shadow areas of the emulsion to adhere to the sheet, and separating said sheet and emulsion layer to transfer only a stratum of said shadow areas of the emulsion layer to said sheet.

2. The process of claim 1 wherein the gelatin tanning Silver halide developing agent and the substantially nontanning silver halide developing agent are present in the emulsion layer before exposure.

References Cited in the file of this patent UNITED STATES PATENTS Chemical Abstracts, 48:8625i (1954).

(Copy in Sci. Lib.) 

1. A METHOD OF PHOTOGRAPHIC REPRODUCTION WHICH COMPRISES EXPOSING TO A TWO-TONE SUBJECT A SUBSTANTIALLY NONHARDENED GELATINO-SILVER HALIDE EMULSION LAYER, SAID EMULSION BEING NOT HARDER THAN A GALATIN LAYER CONTAINING 0.7 GRAM OF FORMALDEHYDE PER POUND OF GELATIN FRESHLY COATED, DEVELOPING SAID EXPOSED EMULSION LAYER WITH A SOLUTION OF POTASSIUM CARBONATE AND ACETAMIDE IN THE PRESENCE OF BOTH A GELATIN TANNING SILVER HALIDE DEVELOPING AGENT AND A SUBSTANTIALLY NON-TANNING SILVER HALIDE DEVELOPING AGENT TO OBTAIN A HARDENED GELATIN AND SILVER IMAGE IN THE AREAS OF THE EMULSION LAYER CORRESPONDING TO THE HIGHLIGHTS OF THE SUBJECT, AND SUBSTANTIALLY UNHARDENED GELATIN, SILVER AND THE SILVER HALIDE IN THE AREAS OF THE EMULSION LAYER CORRESPONDING TO THE SHADOWS OF THE SUBJECT, SAID DEVELOPMENT BEING SUCH AS TO PREVENT ANY SUBSTANTIAL TANNING OF THE EMULSION LAYER IN SAID AREAS CORRESPONDING TO THE SHADOWS OF THE SUBJECT, PRESSING A SHEET HAVING AN ABSORBENT SURFACE AGAINST SAID EMULSION LAYER WHILE SAID EMULSION LAYER IS MOIST TO CAUSE ONLY THE SHADOW AREAS OF THE EMULSION TO ADHERE TO THE SHEET, AND SEPARATING SAID SHEET AND EMULSION LAYER TO TRANSFER ONLY A STREAM OF SAID SHADOW AREAS OF THE EMULSION LAYER TO SAID SHEET. 